U.S. patent number 10,328,405 [Application Number 15/329,457] was granted by the patent office on 2019-06-25 for process for the production of solid cooling agents.
This patent grant is currently assigned to Symrise AG. The grantee listed for this patent is Symrise AG. Invention is credited to Oliver Lenz, Michael Michler, Jorg Niekerken, Jurgen Siewert, Christian Wolter.
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United States Patent |
10,328,405 |
Siewert , et al. |
June 25, 2019 |
Process for the production of solid cooling agents
Abstract
Suggested is a process for the production of solid cooling
agents, wherein a pre-scraped melt, i.e., a melt of menthol
compounds with added seed crystals is applied to a pre-cooled area
by even deposition of drops.
Inventors: |
Siewert; Jurgen (Rollshausen,
DE), Michler; Michael (Eimen, DE),
Niekerken; Jorg (Holzminden, DE), Lenz; Oliver
(Uslar, DE), Wolter; Christian (Ottenstein,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Symrise AG |
Holzminden |
N/A |
DE |
|
|
Assignee: |
Symrise AG (Holzminden,
DE)
|
Family
ID: |
51225444 |
Appl.
No.: |
15/329,457 |
Filed: |
July 26, 2015 |
PCT
Filed: |
July 26, 2015 |
PCT No.: |
PCT/EP2015/067093 |
371(c)(1),(2),(4) Date: |
January 26, 2017 |
PCT
Pub. No.: |
WO2016/016154 |
PCT
Pub. Date: |
February 04, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170216802 A1 |
Aug 3, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Jul 29, 2014 [EP] |
|
|
14179023 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01J
2/26 (20130101); A61K 47/12 (20130101); A61K
9/2013 (20130101); C07C 29/78 (20130101); B29B
9/10 (20130101); C07C 29/78 (20130101); C07C
35/12 (20130101) |
Current International
Class: |
B01J
2/26 (20060101); A61K 9/20 (20060101); A61K
47/12 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
03/101924 |
|
Dec 2003 |
|
WO |
|
2007/071512 |
|
Jun 2007 |
|
WO |
|
2008/152009 |
|
Dec 2008 |
|
WO |
|
2010/095304 |
|
Aug 2010 |
|
WO |
|
Primary Examiner: Ferre; Alexandre F
Attorney, Agent or Firm: Dilworth & Barrese, LLP
Claims
The invention claimed is:
1. A process for the production of a menthol pastille with a curved
side and a flat side, comprising the step of: placing a pre-scraped
melt of menthol compounds with added seed crystals of L-menthol
onto a pre-cooled single steel belt by even deposition of drops,
and wherein the steel belt has cooling zones independently of one
another each having a temperature below the respective melting
point of said L-menthol seed crystals in the range of from about 15
to about 42.degree. C.
2. The process of claim 1, wherein seed crystals are used which
were formed by treatment of the melt to be used in a scraped
surface heat exchanger.
3. The process of claim 1, wherein the menthol compounds are
selected from the group consisting of Menthol, Racemic Menthol,
Menthol Methyl Ether, Menthone Glyceryl Acetal (FEMA GRAS 3807),
Menthone Glyceryl Ketal (FEMA GRAS 3808), Menthyl Lactate (FEMA
GRAS 3748), Menthol Ethylene Glycol Carbonate (FEMA GRAS 3805),
Menthol Propylene Glycol Carbonate (FEMA GRAS 3806),
Menthyl-N-ethyloxamate, Monomethyl Succinate (FEMA GRAS 3810),
Monomenthyl Glutamate (FEMA GRAS 4006), Menthoxy-1,2-propanediol
(FEMA GRAS 3784), Menthoxy-2-methyl-1,2-propanediol (FEMA GRAS
3849) and the menthane carboxylic acid esters and amides WS-3,
WS-4, WS-5, WS-12, WS-14 and WS-30 and mixtures thereof.
4. The process of claim 1, wherein the pre-scraped melt of menthol
compounds has a temperature in the range of from about 40 to about
60.degree. C.
5. The process of claim 1, wherein the pre-scraped melt contains
from about 0.1 to 12 wt. % seed crystals.
6. The process of claim 5, wherein the pre-scraped melt contains
from about 0.1 to about 12 wt. % seed crystals of L-menthol.
7. The process of claim 1, wherein the step of placing a
pre-scraped melt of menthol compounds with added seed crystals of
L-menthol onto a pre-cooled single steel belt occurs by even
deposition of drops from a rotoformer.
Description
FIELD OF THE INVENTION
The invention is in the field of cooling agents, specifically of
menthol and menthol compounds, and relates to a process for the
production of corresponding solid cooling agents, particularly of
flakes or pastilles with improved storage properties and a reduced
tendency to sublime.
STATE OF THE ART
Menthol is an agent occurring in nature, which causes a cooling
effect when brought in contact with mucous membranes, specifically
the oral mucosa. Menthol and numerous subsequently developed
menthol compounds with an, in part, significantly increased cooling
effect are thus widely used in the pharmaceutical, cosmetic and
food industries. Menthol is found in natural sources, for example,
in peppermint oil, in the form of four diastereomeric pairs of
enantiomers of which only the main component, (-)-menthol or
L-menthol, has the desired taste and other sensory properties, as
already described in J. Am. Chem. Soc, Vol. 39 (8), 1917, pp.
1515-1525. Particularly the melting points of these various forms
are between 33 and 43.degree. C., as described in Archiv der
Pharmazie, 307 (7), 1974, pp 497-503. Accordingly, the melting
point of the stable .alpha.-form is between 42 and 43.degree.
C.
Due to this situation of the melting points, L-menthol and most
menthol compounds can be administered to the end user both as a
melt that is kept liquid in heated containers and also in the form
of crystals or other congealed molded bodies such as granular
materials, pastilles, flakes and the like. Generally, all solids
which have a melting point of barely above the ambient temperature
such as L-menthol and the substances that are structurally related
to menthol have a strong tendency to cake and to agglomerate. The
processing of such material that does not comply with the
specification, however, involves a substantial additional effort.
If pure L-menthol or menthol compounds is to be sold as a solid,
i.e., material that has not been treated with additives such as,
for example, separating agents, it must be ensured that the product
will reach the end user in pourable form, either by an unbroken
cold chain or by the way of shaping.
Menthol is commercially available, for example, in the form of
large crystals having a thickness of from 1 to 3 mm at a length of
from 0.5 to 3 cm. They are traditionally grown in small amounts
from naturally obtained peppermint oil, where the oil is allowed to
crystallise in troughs or tubs in cold storage for many days. These
crystals have a ready pourability at a low filling height only, but
they increasingly agglomerate visibly at an increased load and/or
an increased temperature. The technical effort to realize the
crystallisation, the separation and the purification of the
crystals and the low space/time profit of such a long-term process
render it unattractive for industrial use.
DE 2530481 relates to a device for the crystallising of substances,
particularly of optically active menthol compounds which under
crystallisation conditions form coarse needle- or bar-shaped
crystals. The crystallisation process that is to be carried out
discontinuously is performed by means of a particular stirrer that
prevents an agglomeration of the crystals in the crystal
suspension. The valuable product is eventually isolated by a
centrifuge and dried in a dryer.
The two patent specifications U.S. Pat. Nos. 3,023,253 and
3,064,311 describe flaked L-menthol and a process for the
preparation of such flakes by applying a melt of L-menthol onto a
cooled pan roller; however, these mixtures do not contain any seed
crystals. If desired, the menthol melt may be introduced between a
pair of counter-rotating, cooled rollers. The menthol film that has
begun to crystallise on the pan roller is post-processed by
tempering it by means of an introduction of heat, and reinforced by
applying additional menthol. Both post-treatments are obtained
simultaneously by means of a feed roller. Initially, the flakes
such obtained exhibit a good pourability. After longer storage,
however, a slight caking takes place that requires a mechanical
loosening by shaking the container. It is noted that this caking is
caused by a porous surface that is mentioned but not characterised
in more detail and an accompanying heavy sublimation of the
product, and that the product such obtained may be further
processed to pellets by compacting.
The principle of further enlargement of the primary particles by
compacting is also described in DE 10224087, relating to compacted
menthol in the form of menthol pellets as well as a process for the
production thereof. Here, however, the focus is not on the effect
of the particle size alone, but on the fact that the primary
particles must be present in a specific crystal form. On condition
that these predominantly consist of the thermodynamically stable
.alpha.-form that only melts at 42.5.degree. C., it is possible to
obtain granular materials that are resistant against caking by
compressing crystals obtained from solution crystallisation or from
the formation of flakes on cooling rollers.
The subject-matter of the international patent application WO 2008
152009 A1 (BASF) is a process for the production of L-menthol in
solid form by bringing an L-menthol melt into contact with two
cooled surfaces that are spaced apart from one another while the
L-menthol melt is congealing, resulting in L-menthol in solid form,
whereby the contact between the congealing L-menthol melt and the
cooled surfaces is maintained at least until congelation is
completed. In this process, the crystallisation of menthol is
effected by a combination of a pre-crystalliser and a double-belt
cooler. Herein, the menthol suspension is introduced into the gap
between two cooled surfaces and allowed to congeal or
crystallize.
The processes of the state of the art share a number of serious
disadvantages, namely, particularly, a low storage stability.
Directly after storing, the products start to agglomerate, needles
are formed as a result of sublimation, the crystals break as a
result of insufficient mechanical solidity, so that, in sum, the
product according to the specification is not obtained, which gives
rise to various complaints.
The object of the present invention was, therefore, to provide
solid cooling agents, particularly, menthol pastilles, exhibiting a
significantly lower tendency to agglomerate and, particularly,
being less prone to break easily. At the same time, the process
should be carried out such that there is as little caking as
possible during cooling and thus only little product loss.
Eventually, the granular materials or pastilles such obtained are
intended to emit as little residual heat as possible.
DESCRIPTION OF THE INVENTION
The subject-matter of the invention is a process for the production
of solid cooling agents in which a pre-scraped melt, i.e., a melt
of menthol compounds with added seed crystals is placed onto a
pre-cooled area by even deposition of drops.
Surprisingly, it was found that the solid cooling agents obtainable
according to the process of the invention, specifically, the
pastilles, in contrast to the state of the art (a) do not
agglomerate during storage and transport and have a visibly smaller
portion of broken particles; (b) leave significantly less caking on
the cooling belt; (c) have a significantly lower proportion of
fines and thus provide a higher yield; (d) in addition, have curved
surfaces, thus having only few contact points with one another when
poured; (e) have a surface-to-volume ratio, as a result of which
the tendency to sublime is further reduced; (f) have a smaller
tendency to form bridges (low solidification during storage); (g)
emit a low amount of residual heat in the packaging.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described in greater detail with
reference to the accompanying drawings, in which
FIG. 1 is a photograph of pastilles prepared according to Example 1
of the present invention,
FIG. 2 is a photograph of pastilles prepared according to Example 2
of the present invention,
FIG. 3 is a photograph of pastilles prepared according to Example 3
of the present invention,
FIG. 4 is a photograph of pastilles prepared according to Example 4
of the present invention,
FIG. 5 is a photograph of pastilles prepared according to Example 5
of the present invention, and
FIG. 6 schematically illustrates a steel belt cooler with a
Rotoformer and an upstream scraped surface heat exchanger for
producing the pastilles of the examples according to the present
invention.
Menthol and Methol Compounds
Menthol compounds which can be applied within the meaning of the
invention are--besides the basic structure of menthol
itself--products to be solidified, for example, selected from the
group consisting of Menthol Methyl Ether, Menthone Glyceryl Acetal
(FEMA GRAS.sup.1 3807), Menthone Glyceryl Ketal (FEMA GRAS 3808),
Menthyl Lactate (FEMA GRAS 3748), Menthol Ethylene Glycol Carbonate
(FEMA GRAS 3805), Menthol Propylene Glycol Carbonate (FEMA GRAS
3806), Menthyl-N-ethyloxamate, Monomethyl Succinate (FEMA GRAS
3810), Monomenthyl Glutamate (FEMA GRAS 4006),
Menthoxy-1,2-propanediol (FEMA GRAS 3784),
Menthoxy-2-methyl-1,2-propanediol (FEMA GRAS 3849) as well as the
menthane carboxylic esters and amides WS-3, WS-4, WS-5, WS-12,
WS-14 and WS-30 and their mixtures. .sup.1 FEMA stands for "Flavor
and Extracts Manufacturers Association", and GRAS is defined as
"Generally Regarded As Safe". A FEMA GRAS designation means that
the substance marked as such has been tested according to standard
methods and is considered to be toxicologically safe.
A first important representative of the cooling agents is
Monomenthyl Succinate (FEMA GRAS 3810), which has been patented as
a substance by Brown & Williamson Tobacco Corp. (U.S. Pat. No.
3,111,127) already in 1963, and as a cooling agent, which is the
subject-matter of the industrial property rights U.S. Pat. Nos.
5,725,865 and 5,843,466 (V.Mane Fils). Both the succinate and also
the analogous Monomenthyl Glutarate (FEMA GRAS 4006) are important
representatives of monomenthyl esters on the basis of di- and
polycarboxylic acids:
##STR00001##
Examples of applications of these substances can be found, for
example, in the patent specifications WO 2003 043431 (Unilever) or
EP 1332772 A1 (IFF).
The next important group of preferred menthol compounds within the
meaning of the invention comprises carbonate esters of menthol and
polyols such as, for example, glycols, glycerol or carbohydrates
such as, for example, Menthol Ethylene Glycol Carbonate (FEMA GRAS
3805=Frescolat.RTM. MGC), Menthol Propylene Glycol Carbonate (FEMA
GRAS 3784=Frescolat.RTM. MPC), Menthol 2-Methyl-1,2-propanediol
Carbonate (FEMA GRAS 3849) or the respective sugar derivatives:
##STR00002##
The use of such substances as cooling agent for cigarettes is, for
example, the subject matter of the patent specification U.S. Pat.
No. 3,419,543 (Mold et al.) of the year 1968; its use as
physiological cooling substance is claimed in DE 4226043 A1
(H&R).
The menthol compounds Menthyl Lactate (FEMA GRAS
3748=Frescolat.RTM. ML) and, particularly, Menthone Glyceryl Acetal
(FEMA GRAS 3807) or Menthone Glyceryl Ketal (FEMA GRAS 3808) which
is marketed under the designation Frescolat.RTM. MAG are preferred
within the meaning of the invention.
##STR00003##
The former structure is obtained by esterification of lactic acid
with menthol, the latter by acetalisation of menthone with glycerol
(cf. DE 2608226 A1, H&R). This group of compounds also includes
3-(1-Menthoxy)-1,2,propanediol, which is also known as Cooling
Agent 10 (FEMA GRAS 3784, vgl. U.S. Pat. No. 6,328,982, TIC), and
3-(I-Menthoxy)-2-methyl-1,2,propanediol (FEMA GRAS 3849), which has
an additional methyl group.
##STR00004##
The production of 3-(I-Menthoxy)-1,2,propanediol is carried out,
for example, on the basis of menthol according to the following
scheme (cf. U.S. Pat. No. 4,459,425, Takagaso):
##STR00005##
Alternative routes, in which menthol is reacted with
epichlorohydrin in the first step, are described in U.S. Pat. Nos.
6,407,293 and 6,515,188 (Takagaso). In the following, an overview
is provided of the preferred menthol compounds which are
characterized by a C--O bond:
##STR00006##
Among these substances, Menthone Glyceryl Acetal/Ketal as well as
Menthyl Lactate and Menthol Ethylene Glycol Carbonate or Menthol
Propylene Glycol Carbonat have proved to be particularly preferred,
which are sold by the applicant under the designations
Frescolat.RTM. MGA, Frescolat.RTM. ML, Frescolat.RTM. MGC and
Frescolat.RTM. MPC.
In the 1970ies, menthol compounds having a C--C-bond at the 3'
position were developed for the first time, a number of
representatives of which can also be used within the meaning of the
invention. These substances are generally referred to as WS types.
The basic structure is a menthol derivative, where the hydroxyl
group is replaced by a carboxyl group (WS-1). All other WS types
derive from this structure such as, for example, the species WS-3,
WS-4, WS-5, WS-12, WS-14 and WS-30 which are also preferred within
the meaning of the invention. The two following diagrams show the
synthesis pathways:
##STR00007##
The esters that are derivable from WS-1 are described, for example,
in U.S. Pat. No. 4,157,384, and the respective N-substituted amides
in J. Soc. Cosmet. Chem. pp 185-200 (1978).
Not all cooling agents described above are solid at ambient
temperature and may be formed to pastilles, or compacted. However,
it is very well possible to introduce into the process mixtures of
the solid and liquid cooling agents at ambient temperature and to
obtain corresponding solid end products.
Preferred starting materials for carrying out the process according
to the invention are melts of racemic menthol, particularly
preferably of L-menthol, where the melted menthol may be of natural
or synthetic origin and has an enantiomeric excess of typically at
least 95, 96 or from 97 to 100%, preferably, 98, 98.5 or from 99 to
99.9%. Particularly suitable starting materials within the scope of
the process according to the invention are also such melts of
L-menthol which have a content of L-menthol of at least 95, 96 or
97 wt. % or above, preferably, from at least 98 to 100 wt. % and
particularly preferably 98, 98.5 or from 99 to 99.9 wt. % (each
based on the total weight of the melt) besides impurities such as,
for example, residues of solvents, diastereomers of L-menthol or
side products from synthesis or isolation processes.
Here, the term L-menthol melt is preferably understood to be such
L-menthol which is mostly present, i.e., in amount of at least 80,
or better 85 wt. %, preferably at least 90 or 95 wt. %, and
particularly preferably at least 95, 96, 97, 98 or 99 wt. % in
melted form, wherein the remaining weight proportions make up the
amount of solid L-menthol in the melt. Herein, the proportion of
solid menthol optionally contained in the melt may be such that it
is still present in the melt due to a not completely finished
melting process of the material used in the melt to provide the
melt, or it is added to the completely or partly melted menthol in
solid form, for example, in the form of crystals of L-menthol in
the .alpha.-form. Such crystals of L-menthol in the .alpha.-form,
which are also referred to as seed crystals, can also be obtained
in a conventional approach, for example, by crystallisation of
L-menthol from a solution or a melt containing L-menthol.
Within the scope of a preferred form of embodiment, such crystals
of L-menthol in the .alpha.-form are used which are obtained by
treating the L-menthol melt to be used according to the invention
in a scraped-surface heat exchanger, as a result of which the seed
crystals are formed in situ in the L-menthol melt that is to be
solidified, avoiding an additional process step.
Ways of Carrying Out the Process
Within the meaning of the process according to the invention, a
pre-scraped melt of a menthol compound is fed, for example, to a
so-called Rotoform system by means of a pump.
In order to ensure a possibly complete congelation of the melts,
preferably, of L-menthol in the .alpha.-form, seed crystals are
added to the melt before feeding it to the Rotoformer and applying
it onto the cooling belt, as described above. For example, this can
be obtained by stirring previously comminuted crystals, for
example, of the .alpha.-form of the L-menthol, into a feed vessel,
or sprinkling them onto a used L-menthol melt (the liquid crystal
film). Alternatively, it is possible to sprinkle .alpha.-menthol
crystals onto the cooling belt. In a preferred embodiment of the
invention, seeding is obtained by allowing the melt to pass through
a heat exchanger that is operated below the melting point, where
adhering crystallised material is scraped off the walls by a
scraping means. The skilled person is familiar with such
arrangements which are, for example, referred to as "scraped
surface heat exchangers" and which are described in G. Arkenbout:
"Melt Crystallization Technology", Technomic Publishing Co. 1995, p
230. Accordingly, a preferred embodiment of the process according
to the invention is characterized in that the seed crystals are
formed as a result of treating the melts to be used in a scraped
surface heat exchanger.
A pre-scraped melt of menthol compounds which has a temperature in
the range of from about 40 to about 60.degree. C. and particularly
of from about 43 to 50.degree. C. and/or containing from about 0.1
to 12 wt. %, particularly from about 1 to about 5 wt. % seed
crystals is preferably used. Particularly preferred is the use of a
pre-scraped melt which contains from about 0.1 to 12 wt. % seed
crystals of L-menthol. Also, menthol melts that have been
undercooled to temperatures of from 42 to 43.degree. C. can be
used. In order to prevent cakings from forming in the scraped
surface heat exchanger, which then peel off uncontrolledly, thus
influencing the melting temperature, it is recommended to equip the
heat exchanger with, for example, a trace heating.
In a particularly preferred embodiment of the invention, uniform
drop deposition is performed by means of a so-called Rotoformer.
The Rotoformer consists of a heated cylindrical internal body,
which is supplied with liquid product, and an external tube that is
equipped with numerous perforations, which concentrically rotates
around the inner body, depositing drops of product on the whole
length of a steel belt cooler in the process. A system of baffles
and nozzles built into the internal body ensures an even pressure
over the whole width of the component and thus a uniform exit of
product through all perforations of the external tube. Here, all
products, specifically the pastilles such obtainable, are of a
uniform size from one edge of the steel belt to the other. The
circumferential speed of the Rotoformer is preferably synchronous
with the speed of the belt: therefore, the drops are deposited
without deformation. The heat released during solidification and
cooling is transferred from the stainless steel belt to the cooling
water, which is sprayed against the underside of the belt. The
water is collected in tanks and guided to the re-cooling system, at
no stage it comes into contact with the product. After depositing
the drop on the steel belt, a small amount of product will remain
attached to the outer rims of the perforations of the external
tube. A heatable refeed bar presses this product into an inner gap
within the Rotoformer, from where it is mixed with original product
and re-deposited onto the steel belt. To prevent the Rotoformer
from plugging, for example, the use of a heat accumulation hood is
recommended here. Corresponding combinations of Rotoformer and
steel belt coolers are commercially available, for example, from
the company Sandvik Process Systems GmbH, D-70736 Fellbach. A very
similar technology is offered under the name Rollomat, for example,
by the company Kaiser Process & Belt Technology GmbH, D-47800
Krefeld. Rotating and vibrating perforated plates are suitable, in
principle, provided that the viscosity (according to the solids
content in the melt) of the melt droplets is not too high.
Preferably, the melt drops are deposited by the Rotoformer onto a
cooled belt, particularly, a cooled steel belt which may have a
plurality of cooling zones, which can be tempered independently of
one another, for example, to temperatures of below the melting or
congelation point, which for L-menthol is in the range of from
about 5 to about 42.degree. C. Typical, for example, are cooling
belts with three cooling zones of which the first two have
temperatures of from about 25 to 30, and the last one of from about
15 to 20.degree. C. For example, cooling belts are used which have
a length of from about 2 to about 20 m and a width of from about 10
to about 200 cm. The speed of operation of the cooling belts is
advantageously set such that, in consideration of the above
mentioned geometry of the belts, a cooling time ensuring a complete
crystallisation of the melts is maintained in this manner.
Depending on the desired capacity, also larger units can of course
be used, where the capacity is proportional to the width of the
cooling belt and the duration time is a result of the length and
the speed of the cooling belt. In principle, the process can also
be performed on plants having a system capacity of from 50 to 1,000
kg/h or more.
Subsequently, the solid cooling agents are scraped from the belt,
which is, for example, performed by means of a knife. In doing so,
scraping can be performed either after the simple cooling period or
with the aid of belt rewind after a further stay on the cooling
belt close to the point of deposition. The material may stay longer
on the belt to allow ripening and remain in an undertempered or
post-tempered area.
Instead of a cooling belt, also disk pastillators or similar can be
used, such as, for example, pastillating aids sold by the company
Andritz Gouda, NL-2740 Waddingxveen.
The object of the process is to provide solid cooling agents that
are crystallised as completely as possibly and which remain
mechanically stable during storage. In doing so, it is to be
considered that also the thermodynamically most stable form of
L-menthol sublimes. As sublimation is a process at the surface of
the particles, it is advantageous if the particles exhibit a small
surface-to-volume ratio. The reason is that bridge connections
between the particles are formed by sublimation during storage,
which explains the caking. In addition, particles with partly
curved surfaces are preferred, in which there are less contact
points during pouring.
Within the scope of the present invention--as far as it relates to
L-menthol as ingredient--the congelation or crystallisation of the
L-menthol melt used is preferably considered completed if the
contained L-menthol is present in solid form to at least about 80
wt. %, or better from 85 to 100 wt. %, preferably, from 90 to 100
wt. %, preferably, 95 or from 97 to 99.5 wt. %, and particularly
preferably from 98 to 99 wt. % in the .alpha.-form. Such L-menthol
exhibits changes only to a small extent by changing the material
into the thermodynamically most stable form and thus changes with
respect to its surface condition only to a small extent, if at
all.
The particles according to the invention are characterised in that
they contain only a low proportion of fines, exhibit a favourable
surface/volume ratio and simultaneously have curved, but flat
surfaces, which when poured result in contact areas that are as
small as possible and that are resistant against abrasion, and, in
addition, exhibit as few breaking edges as possible or none at
all.
A further preferred subject-matter of the invention thus relates to
menthol particles in the form of pastilles with a curved and a flat
side, having a diameter of from about 1 to about 20 mm, preferably,
5 to 12 mm, and are furthermore characterized in that they (i) have
a proportion of fines (i.e. a proportion of particles with an
average diameter smaller than 1.6 mm) of less than 5 wt. %,
preferably less than 2 wt. % and more preferably less than 1 wt. %,
particularly preferably less than 0.5 wt. %, especially preferred
less than 0.1 wt. %, and/or (ii) have an alpha-menthol content of
at least 80 wt. %, preferably from about 85 to about 99 wt. % and
particularly preferably from 90 to about 95 wt. %; and/or (iii)
have a surface-to-volume ratio of less than 2:1/mm, preferably less
than 1.5:1/mm and particularly preferably less than 1.0:1/mm. (iv)
have curved surfaces so that the ratio of plane surface to the
total surface of the particle is 60% maximum, preferably less than
50%, and more preferably less than %.
The form of the obtained solidified L-menthol present in each case
and thus the completion of the congelation process can be
determined by processes known to the skilled person such as x-ray
diffraction or powder diffractometry (see, for example, Joel
Bernstein, "Polymorphism in Molecular Crystals", Oxford University
Press 2002, pp 94-150).
INDUSTRIAL APPLICABILITY
A further subject-matter of the invention relates to cooling agents
in solid form which are obtainable according to the process
described above and present in the form of flakes or, preferably,
pastilles. By means of the process according to the invention, for
example, the production of pastilles with diameters of from about 1
to about 20 mm, preferably from about 5 to about 12 mm, this is
possible without any problem. As the particles are also to be
brought into solution after storage, the particle size indicated is
an optimum balance between solubility on the one hand and an
inclination to cake on the other.
These cooling agents also, preferably, share the property that they
(i) have a proportion of fines (i.e., a portion of particles with
an average diameter of less than 1.6 mm) of less than 5 wt. %,
preferably less than 2 wt. % and more preferably less than 1 wt. %,
particularly preferably less than 0.5 wt. %, especially preferred
less than 0.1 wt. %, and/or (ii) have an alpha-menthol content of
at least 80 wt. %, preferably from about 85 to about 99 wt. % and
particularly preferably from about 90 to about 95 wt. %; and/or
(iii) have a surface-to-volume ratio of less than 2:1/mm,
preferably less than 1.5:1/mm and particularly preferably less than
1.0:1/mm. (iv) have curved surfaces, so that the ratio of plane
surface to the total surface of the particle is 60% maximum,
preferably less than 50% and more preferably less than 40%.
A last subject-matter of the present invention is the use of the
solid cooling agents or the menthol particles in cosmetic or
pharmaceutical preparations and foods.
EXAMPLES
Examples of Production
In the following examples of embodiment it was intended to
determine how the production of pastilles with an optimum
surface-to-volume ratio and good caking properties are to be
produced and examined. Also, it was intended to determine process
conditions ensuring the production of completely crystallised
material. Any post-crystallisation in the packaged state should be
avoided.
Test Set Up and Performance of the Process
The tests were performed on a steel belt cooler with a Rotoformer
and an upstream scraped surface heat exchanger as schematically
illustrated in FIG. 6. Here, the reference signs mean the
following:
TABLE-US-00001 1 Educt container 2 Educt pump 3 Extruder 4 Heat
exchanger 5 Valve 6 Re-feeding of educt 7 Rotoformer 8 Cooling belt
with three cooling zones T1, T2, T3 9 Granulator 10 Product
deposition
In doing so, a melt that has been pre-scraped in the scraped
surface heat exchanger (i.e., a suspension of seed crystals in
menthol) was deposited onto a pre-cooled steel belt by means of a
Rotoformer. The length of the cooling belt was 12.5 m, the width of
the belt was 600 mm. The cooling belt had three cooling zones which
could be tempered independently of one another. Scraping from the
cooling belt was performed by knife, either after a single cooling
period or with the aid of of the belt rewind near the deposition
location. In doing so, the material was subjected to additional
cooling on the 12.5 m of the belt rewind. The speed of operation of
the cooling belt (and thus the capacity of the cooling belt) was
changed only insignificantly in the course of the tests, as a
result of which an output in the range of from 150-165 kg/h during
the tests was obtained. The material obtained was separated from
attached fines by means of a vibrating screen (company Allgaier;
sieve hole width: 1.6 mm and 1.25 mm). The deposition temperature
of the material was determined by measurement in a Dewar vessel
using a thermocouple element. The change of temperature after
scraping from the belt will in the following be referred to as
post-crystallisation heat. Output was determined with a stopwatch
and a scale at the middle part of a test run. For each test, about
20 to 30 kg pastilles were removed as initial forerunnings. The
materials obtained were packed into F1 cardboard boxes with a PE
inner bag--(Symrise standard packaging means for compacted menthol)
during the test.
Example 1
A starting temperature of 30.degree. C. was selected for T1 and T2,
as this temperature of the metal belt is near the congelation
temperature of the .alpha.-form (see FIG. 1) and only a small
amount of .gamma.-form could be expected at a superposed
spontaneous crystallisation. The congelation temperature in the
pastille should be higher as a result of an inferior heat transfer
through the congealed menthol and should thus, preferably, lead to
the formation of the .alpha.-form. At T3, 15.degree. C. were
selected to increase the heat transfer through the already
solidified menthol thus ensuring a complete crystallisation. The
test conditions are reflected in Table 1.
TABLE-US-00002 TABLE 1 Test conditions Temperature zones of the T1:
30.degree. C.; T2: 30.degree. C.; T3: 15.degree. C. cooling belt
Temperature of the scraped 41.5.degree. C. surface heat exchanger
Output 150 kg/h Weights (cardboard boxes) 15.6 kg/12.45 kg/19.50
kg/21.05 kg/20.6 kg Fines 41.8 g per 89.2 kg (469 g/t pastilles)
Deposition temperature 25.2.degree. C. Post-crystallisation heat
1.degree. C. over 1 h Room temperature: 27.degree. C.
After removing small forerunnings, pure white pastilles were
obtained (FIG. 1). The pastilles were completely crystallised and
difficult to split with a spatula/knife.
Example 2
After passing the cooling belt, the pastilles were not completely
crystallised at T2. At the end of the cooling belt at T3, the
pastilles were slightly soft at the upper end and easily splittable
with a knife. The test conditions are reflected in Table 2; the
pastilles are shown in FIG. 2.
TABLE-US-00003 TABLE 2 Test conditions Temperature zones of the T1:
30.degree. C.; T2: 30.degree. C.; T3: 18.degree. C. cooling belt
Temperature of the scraped 41.4-41.6.degree. C. surface heat
exchanger Output 165 kg/h Weights (cardboard boxes) 19.82 kg/20.48
kg/20.93 kg/20.27 kg Fines 106.4 g per 81.5 kg (1305 g/t pastilles)
Deposition temperature 24.4.degree. C. Post-crystallisation heat
1.degree. C. over 30 min Room temperature: 27.degree. C.
Example 3
In the course of test 3, the scraper knife at the end of the
cooling belt was removed. The belt rewind was used as an additional
post-cooling section. The pastilles were hard and fully
crystallised after scraping. The test conditions are reflected in
Table 3; the pastilles are shown in FIG. 3.
TABLE-US-00004 TABLE 3 Test conditions Temperature zones of the
cooling belt T1: 30.degree. C.; T2: 30.degree. C.; T3: 18.degree.
C.; belt rewind post- cooling Temperature of the scraped surface
heat 41.4-41.6.degree. C. exchanger Output 165 kg/h Weights
(cardboard boxes) 20.57 kg/20.49 kg/19.36 kg Fines 48.6 g per 60.42
kg (804 g/t pastilles) Deposition temperature 24.4.degree. C.
Post-crystallisation heat 1.degree. C. over 30 min Room
temperature: 27.degree. C.
Example 4
The pastilles were comparable to example 1. The test conditions are
reflected in Table 4; the pastilles are shown in FIG. 4.
TABLE-US-00005 TABLE 4 Test conditions Temperature zones of T1:
30.degree. C.; T2: 30.degree. C.; T3: 15.degree. C. the cooling
belt Temperature of the scraped 41.5-41.6.degree. C. surface heat
exchanger Output 150 kg/h Weights (cardboard boxes) 18.85 kg/18.75
kg/19.45 kg/19.65 kg Fines 106.1 g per 76.7 kg (1383 g/t pastilles)
Deposition temperature 25.2.degree. C. Post-crystallisation heat
1.0.degree. C. over 30 min Room temperature: 28.degree. C.
Example 5
In the course of example 5, the scraper knife at the end of the
cooling belt was removed. The belt rewind was used as an additional
post-cooling section. The pastilles were hard and fully
crystallised after scraping. The test conditions are reflected in
Table 5; the pastilles are shown in FIG. 5.
TABLE-US-00006 TABLE 5 Test conditions Temperature zones of the
cooling belt T1: 30.degree. C.; T2: 30.degree. C.; T3: 15.degree.
C.; belt rewind post-cooling Temperature of the scraped surface
heat 41.4-41.6.degree. C. exchanger Output 165 kg/h Weights
(Kartons) 15.4 kg Deposition temperature 22.2.degree. C.
Post-crystallisation heat 1.0.degree. C. over 30 min Room
temperature: 28.degree. C.
Example 6
Comparison Example V1
Example 1 was repeated, cooling, however, was performed by means of
a double belt cooler with cooled steel surfaces and a gap width of
0.3 cm (length 12 m, width 35 cm). The double belt cooler also had
3 cooling zones (30.degree. C., 30.degree. C., 15.degree. C.); the
product was scraped off in the form of flakes by means of a
knife.
5 kg each of the pastilles of example 1 according to the invention
(diameter: 5 mm) and of the comparison example V1 were filled into
bags of synthetic material which were stored in cardboard boxes at
20.degree. C. for a period of 6 weeks. The results are summarised
in Table 6.
TABLE-US-00007 TABLE 6 Storage tests Storage time Example 1
Comparison example V1 1 week Material easily separable at the
Material easily separable at the surface. surface. No
agglomeration. No agglomeration. 2 weeks Material easily separable
at the Material separable at the surface. In the surface. In the
centre of the filling, a centre of the filling there are small
amount cakes to form agglomerations which are separable by
agglomerations which are manually means of a shovel. separable. 3
weeks Material easily separable at the Material separable at the
surface. In the surface. In the centre of the filling, a centre of
the filling there are distinct small amount cakes to form
agglomerations which are separable by agglomerations which are
manually means of a shovel. separable. 4 weeks Material easily
separable at the Material is separable at the surface. In surface.
In the centre of the filling, a the centre of the filling there are
distinct small amount cakes to form agglomerations which are
separable by agglomerations which are manually means of a shovel.
separable. 5 weeks Material is separable at the surface. In
Material difficult to separate at the the centre of the filling
there are surface. In the centre of the filling there
agglomerations which are separable are distinct agglomerations,
which are by means of a shovel. separable by means of a shovel. At
the surface, slight formation of needles due to sublimation. 6
weeks Material is separable at the surface. In 80% is agglomerated,
distinct formation the centre of the filling there are of needles
due to sublimation. distinct agglomerations, which are separable by
means of a shovel. At the surface, slight formation of needles due
to sublimation.
Example 7
In order to prove that the crystal form alone is not decisive for
the inclination to cake, 20 kg of 8 L-menthol that had been stored
for 8 months and which was completely present in its .alpha.-form,
were comminuted by means of a seave mill with a 3 mm sieve hole
insert to obtain crystal powder. In doing so, no increase in
temperature as a result of the comminution process was measured.
Subsequently, the crystal powder was stored again. Already after
two weeks the powder was caked, forming a block which could only be
loosened locally by heavy kneading.
* * * * *